Related

Blizzard and coastal-flood warnings have been posted from New York City to Rockland, Maine – a wide ground zero for the merger of two powerful winter storms that forecasters say could yield a single storm of historic proportions.

Looking at the snowfall forecasts, Robert Oravec, a senior forecaster at the National Weather Service's Hydrometeorological Prediction Center in College Park, Md., says, "the totals will be huge."

While the warnings cover a long stretch of the Northeastern Seaboard, southern New England and Long Island currently are expected to bear the brunt of the nor'easter – an offshore storm whose counterclockwise circulation brings moisture-laden winds ashore out of the northeast.

The warnings take effect at 6 a.m. Friday and run through 1 p.m. The National Weather Service defines a blizzard as at least three hours of winds blowing at 35 miles an hour or higher with falling or blowing snow cutting visibility to a quarter of a mile or less.

Forecasters with the National Weather Service expect snowfall to range from 18 to 24 inches through the vast majority of areas covered by the warning. But some spots could receive as much as 36 inches from the most intense pockets of precipitation embedded in the storm.

This weekend's nor'easter will be the product of a winter storm currently moving through the Great Lakes region and a storm currently centered over Georgia.

Overnight, the storm over Georgia will move out over the Atlantic and begin traveling up the coast. It is expected to begin interacting with the system moving east from the Great Lakes late Friday morning, with the explosive intensification occurring overnight Friday and into Saturday morning, "producing the very heavy snow and high winds," Mr. Oravec says.

Currently, the forecast for Friday and Saturday includes winds of 30 to 40 miles an hour, with gusts up to 65 miles an hour. Off the coast, those winds are expected to whip up waves averaging 30 feet high, although individual waves could top 60 feet.

Many sections of the coast affected by the storm are expected to see a storm surge of from two to three feet, topped by storm-whipped surf. According to the National Weather Service's Ocean Prediction Center, the western end of Long Island Sound could see some of the highest surge, at four to five feet.

For Boston, the storm could elbow its way onto the list of the 10 most intense winter storms on record. Among them: the Blizzard of 1978, which dumped 27.1 inches of snow on Boston 35 years ago this week.

It came on the heels of a storm that struck three weeks earlier and dumped 21 inches of snow on Boston. The Blizzard of '78, which lasted 33 hours, packed sustained winds of 86 miles an hour with gusts reaching 111 miles an hour.

Damage from the '78 blizzard reached $520 million at the time, or nearly $2 billion in 2012 dollars. Some 2,000 homes were damaged, many of them along a coastline experiencing a powerful storm surge on top of a spring tide, when moon and sun line up with respect to Earth in a way that increases the height of high tide and decreases the height of low tide. The Red Cross put the death toll from that storm at 99 people.

This weekend's looming storm first appeared about five or six days ago in a weather model operated by the European Center for Medium Range Forecasting, based in Britain, says Oravec.

That model "has been very reliable in advertising potentially big storm systems that affect the East Coast," he says.

Other models, including those run in the United States, didn't catch on to the potential for the storm until later. Now, "all of the models are in very good agreement that there will be a major blizzard," he says.